A typical conventional creasing device comprises two rotary shafts provided one over the other to extend parallel to each other, a plurality of male creasing rolls mounted on the lower rotary shaft so as to be axially positionable, and a plurality of female creasing rollers as backing rolls each corresponding to one of the male creasing rolls and mounted on the upper rotary shaft so as to be axially positionable, whereby when a corrugated sheet is fed between the male creasing rolls and the female creasing rolls, creases are formed in the sheet by pressing ribs formed on the outer periphery of the male creasing rolls against the sheet (Patent document 1).
In such a creasing device, when forming creases in relatively thick corrugated sheets, such sheets tend to be pressed too hard by the creasing rolls, so that liners forming the surface layers of such sheets tend to crack near the creases. When forming creases in relatively thin corrugated sheets, because such sheets are pressed too weakly by the creasing rolls, no clear creases are formed, so that such sheets cannot be folded along the creases with high accuracy. Thus, such creasing devices include means for adjusting the distances between the male creasing rolls and the female creasing rolls according to the thickness of the corrugated sheet.
In a typical known creasing device of which the distances between the rolls is adjustable, at least one of the upper and lower rotary shafts has both ends thereof rotatably supported by eccentric bearings, whereby by rotating the eccentric bearings and thus rotating the axis of the one of the rotary shafts, the distances between the axes of the upper and lower rotary shafts is adjustable.    Patent document 1: JP Patent Publication 2001-30376A